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- PV power conditioning system using a three-phase multilevel pulse width modulation inverter employing cascaded Scott transformersPublication . Fernao Pires, Vitor; Foito, Daniel; Cordeiro, ArmandoVoltage source inverters (VSIs) are power converters that are considered essential in grid connected photovoltaic (PV) generators. There are several types of topologies for these converters. However, from the point of view of high-quality AC output voltage, multilevel inverters are considered the most adequate. Under this context, this study proposes a new structure for the three-phase DC-AC conversion stage for a grid-connected PV system. It consists of two four-leg two-level voltage source inverters that are connected to two PV generators. These inverters are associated with two Scott transformers. The secondary windings of the transformer are connected in a way that allows a series connection. Due to this, a multilevel operation will be achieved. The performance of the proposed power conditioning system will be verified through simulation and experimental results.
- Fault-tolerant three-phase quasi-switched boost inverterPublication . Cordeiro, Armando; Fernao Pires, Vitor; Foito, Daniel; Bondarenko, OleksandrThis paper proposes a fault-tolerant topology based on the three-phase quasi-switched Boost Inverter ( qSBI ). Besides the additional qSBI, the solution also uses non-active power devices to reconfigure the topology and maintain the normal operation in case of an open-circuit failure mode of a power device. The proposed topology presents important features such as boost capability, avoids extra inductors, capacitors or active power devices. Regarding the control solution for this topology, it will be used on a closed-loop current controller at which be associated a vectorial voltage modulator. Since this modulator is also function of the shoot-through will be possible to recover the amplitude voltage space vectors due to failures in power devices. The combination of these elements allows to obtain three-phase balanced AC currents with reduced total harmonic distortion even in fault-tolerant operation mode. The fault tolerance performance of this solution will be confirmed through several simulation results.
- Three-phase multilevel inverter for grid-connected distributed photovoltaic systems based in three three-phase two-level invertersPublication . Fernao Pires, Vitor; Cordeiro, Armando; Foito, D.; Silva, J. FernandoA multilevel three-phase voltage source inverter (VSI) for distributed grid-connected photovoltaic system is proposed in this paper. This multilevel inverter is based on a new topology using three three-phase two-level VSIs ((TVSI)-V-3) with isolation transformer. The photovoltaic panels are connected at the DC side of each three-phase VSI. The three-phase VSIs AC sides are connected to the three-phase isolation transformer with primary open-end windings, ensuring multilevel operation. The (TVSI)-V-3 can be modulated using existing multilevel Pulse Width Modulation (PWM) schemes. A control system designed to ensure the transfer of the energy generated by the PV generators to the grid is also presented, together with a Phase Disposition PWM (PDPWM) adapted for the multilevel (TVSI)-V-3. Tests of the grid-connected PV multilevel (TVSI)-V-3 will be shown through simulation and experimental results. Several results obtained from experiments confirm the expected characteristics of the multilevel (TVSI)-V-3 photovoltaic system.
- Fault-tolerant SRM dive with a diagnosis method based on the entropy feature approachPublication . Fernao Pires, Vitor; Amaral, Tito; Cordeiro, Armando; Foito, Daniel; Pires, Armando J.; Martins, JoaoThe power electronic converter design is essential for the operation of the switched reluctance motor (SRM). Thus, a fault-tolerant power converter is fundamental to ensure high reliability and extend the drive operation. To achieve fault tolerance, fault detection and diagnosis methods are critical in order to identify, as soon as possible, the failure mode of the drive. To provide such capability, it is proposed in this paper a new fault-tolerant power converter scheme combined with a fault detection method regarding the most common power semiconductors failures in SRM drives. The fast and reliable proposed diagnosis method is based on the entropy theory. Based on this theory, normalized indexes (diagnostic variables) are created, which are independent from the load and speed of the motor. Through this method, it is possible to identify the faulty leg, as well as the type of power semiconductor fault. To test and evaluate the proposed solution several laboratory experiments were carried out using a 2 kW four-phase 8 / 6 SRM.
- A DC-DC converter for bipolar DC microgrids with voltage balance capability to supply a multilevel SRM drivePublication . Fernão Pires, V.; Foito, Daniel; Pires, A. J.; Cordeiro, Armando; Martins, J. F.In this work it is proposed a DC-DC converter to supply a multilevel Switched Reluctance Machine (SRM) drive. The proposed converter was designed to be integrated in a bipolar DC microgrid. Usually, this kind of microgrid requires a support to avoid unbalances between the poles. Thus, the proposed converter also integrates voltage balance capabilities allowing the required support to the bipolar DC microgrid. Besides that, the converter can also supply the drive using only one of the poles. The behavior and operating modes of the converter will be described in detail. Several simulation tests will also be provided. From these tests, the behavior and the several operation modes of the DC-DC as well as the multilevel SRM drive supplied by this converter will also be presented and analyzed.
- Bidirectional boost/buck quadratic converter for distributed generation systems with electrochemical storage systemsPublication . Pires, V. Fernão; Foito, D.; Cordeiro, ArmandoThe increasing number of distributed generation systems using renewable and non-conventional energy sources show the trend of future generation systems. Most of these systems require power electronic converters as an interface between the DC voltage buses and electrochemical storage systems. Such storage systems, like batteries or supercapacitors, usually need bidirectional DC-DC converters to allow their charge or discharge according with necessary operation conditions. In this paper, a non-isolated bidirectional Buck-Boost converter with high voltage gain for electrochemical storage devices used in distributed generation systems is presented. To achieve high voltage gain ratios, the proposed topology presents quadratic characteristics in both step-down (Buck) and step-up (Boost) operation modes. In addition to the wide conversion range, it presents continuous input and output current, reduced charging/discharging ripple and simple control circuitry. All these features allow the energy exchange smoothly and continuously resulting in a longer durability of storage devices. The principle of the operation of the proposed converter in both operation modes, as well as their theoretical analysis will be discussed. The performance of this bidirectional power converter is confirmed through simulation and experimental results.
- Multilevel converter with fault-tolerant capability for the switched reluctance machinePublication . Fernão Pires, V.; Cordeiro, Armando; Foito, Daniel; Pires, A. J.Many critical systems require permanent operation even in a situation of a fault. In this way, electrical drives that are associated to these systems must have fault-tolerant capability. One of the machines that are used in many systems is the switched reluctance machine (SRM). To achieve the best performance with a wide speed range, multilevel converters are one of the adopted options. Thus, this paper presents a new multilevel converter for the SRM with fault-tolerant capability. The proposed solution allows to maintain the drive at operation for both conditions of opencircuit and short-circuit power semiconductor fault. Their operation in normal and fault-tolerant modes for the 8/SRM is presented in detail. To verify the capability and operation modes of the proposed system several simulation tests will be presented.
- Three-level NPC dual-buck inverter designed to safety-critical applicationsPublication . Cordeiro, Armando; Fernao Pires, Vitor; Foito, DanielThis paper presents a three-phase three-level NPC (neutral point-clamped) Dual-Buck inverter topology suitable to increase fault-tolerant capability to safety-critical applications. Using the proposed topology, it is possible to achieve energy processing capability in case of several failure modes. The faulttolerant enhancements are a consequence of appropriate modifications in the control strategy and from redundancy of power devices to maintain the correct operation of the converter. The proposed control strategy adopted in the presented solution can also equalize the capacitor voltages automatically. Some simulation results are included in this study to confirm the validity of the theoretical study.
- Using power electronics and automation to simulate solar PV systemsPublication . Fonte, Pedro M.; Cordeiro, Armando; Barata, Filipe; Pires, V. Fernão; Chaves, Miguel; Foito, Daniel; Gamboa, PauloThis paper presents a solar photovoltaic panel simulator system with the ability to perform automatic tests in different condition according to manufacture parameters. This simulator is based on three buck--boost DC -DC converters controlled by a microcontroller and supported by a AXC 1050 Programmable Logic Controller from Phoenix Contact which is responsible for running the automatic tests. This solution allows to understand the typical operation of solar photovoltaic panels and MPPT algorithms considering suddenly changes in the irradiation, temperature, or load.
- Control of PV distributed systems based on three-phase triple inverters to support grids with unbalanced loadsPublication . Fernão Pires, V.; Foito, Daniel; Cordeiro, Armando; Silva, J. FernandoThis paper is focused on the control system for photovoltaic (PV) generators using three-phase triple inverters. These inverters allow for a distributed PV system, and at the same time, they provide AC multilevel operation. The proposed controller is designed to allow the operation of the inverter in a way that it can extend support to the grid with ancillary services. One of the ancillary services that the three-phase triple inverter can support is the injection of unbalanced currents in order to eliminate or attenuate grid load unbalances. Therefore, the proposed topology will be extended to accommodate four wires. The capability of the system to support the grid with ancillary services, especially the compensation of unbalanced loads, the four-wire multilevel topology operation and the proposed controller will be verified through several simulation tests.